The present invention relates generally to method and apparatus for producing clean perforations in wells and particularly to method and apparatus which provide sand control while displacing well fluids within a cased borehole in the area to be perforated with fluids which are compatible with perforations.
When an oil well casing is perforated in the presence of well fluids containing colloids and other particulate matter for pressure control, the perforation in the oil-bearing formation is often sealed with a filter cake. The prior art has recognized that it is desirable to displace the fluids in the area of the perforation with so-called "completion fluids" in order to produce clean perforations. Typical of such prior art is U.S. Pat. No. 3,138,206 to George H. Bruce et al; U.S. Patent No. 2,842,205 to Allen et al; and U.S. Pat. No. 2,963,088 to Corley. For example, in the Bruce et al patent, the completion fluid is pumped from a reservoir into the annulus between the perforating section and the casing to be perforated. This device attempts to cause the displaced well fluid to be pumped down to the open lower end of the perforating section and up through the interior of a packer and out into the annulus above the packer. However, such a device as is shown in the Bruce et al reference is quite complex and expensive to fabricate. Furthermore, in the Bruce et al system, the compatible fluid is introduced into the annulus above the perforator and is thus dependent upon the displaced fluid being pumped down the annulus and then back up through the interior of the perforator. Thus, the interior of the perforator has to be modified to provide a tortuous path around the shaped charges within the gun. It should also be appreciated that the Bruce et al apparatus is dependent upon extremely intricate piping to maintain a separation between the well fluids and the compatible perforating fluid.
The prior art has also used gravel packing processes, for example, U.S. Pat. No. 3,362,475 to J. L. Huitt et al, to provide sand control for producing formations. However, such processes have hereto been run separate from the perforating process, thus requiring two trips into the well.
It is therefore the primary object of the present invention to provide a new and improved method and apparatus for practicing sand control while displacing the well bore fluid in the area of the casing to be perforated with a fluid which is compatible with such perforations;
It is another object of the invention to provide a combined gravel packing and perforating apparatus for use during a single trip into a well bore; and
It is yet another object of the invention to provide a new and improved method and apparatus for practicing sand control while displacing well bore fluid with compatible perforating fluid without necessarily modifying the interior of the perforating gun.
These and other objects of the present invention are accomplished, generally, by a method and apparatus which utilizes a shield around a perforating apparatus and which utilizes a sand control medium in the annulus between the shield and the perforating apparatus to provide sand control. Means are also provided to pump a compatible perforating fluid through such sand control medium and out through a lower port in the shield to displace the well bore fluid along the length of the perforating apparatus